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Irrigated rice is planted in half the world’s rice fields, and produces about 75% of the world’s rice supply. In adaptation to climate pressures in coming decades this irrigated rice will, however, need to be produced with less water. There is a risk that under alternative irrigation management (AIM) N2O emission offsets the reduction of CH4 emission when N fertilizer is applied at a high rate. A particular challenge is to upscale the often detailed field observations of full greenhouse gas (GHG) budgets to regional or national scales. We are convinced that the only way forward is to fundamentally improve knowledge on key paddy soil biogeochemical processes, which then needs to be synthesized in mechanistic models. The GreenRice project focuses on young floodplain soils, dominant in major river delta. We attribute the status-quo of knowledge on the balance of methanogenic and methanotrophic activity and sources of N2O production to the limited account for the spatial differentiation of microbial processes involved in experimental work, though crucial under AIM. With several specific field- and mesocosm experiments we aim:• to reveal determining factors controlling the rate of change of the soil redox potential in young floodplain paddy soils.• to further our insight how CH4 production in paddy soils under CF as compared to AIM results from the net result of CH4 genesis and oxidation to quantify the release of fixed-NH4 +, expected to be substantial in floodplain soils• to examine the contribution of different N sources to N2O production under AIM• to translate new knowledge generated in GreenRice on specific effects of AIM on GHG emissions in floodplain soils into the DNDC biogeochemical model